design of weapon bays for stealth aircrafts...3 © cranfield university 2017 weapon bay aerodynamics...

© Cranfield University 20171

www.cranfield.ac.uk

DESIGN OF WEAPON BAYS FOR STEALTH AIRCRAFTS

David Bacci


Next Generation Combat Aircraft Design Requirements

► LOW OBSERVABILITY

► TRANSONIC AND SUPERSONIC PERSISTENCE

► STRUCTURAL AND AERODYNAMIC OPTIMISATION OF GEOMETRY

ARMAMENT

CARRIED INSIDE

THE AIRFRAME


Weapon Bay Aerodynamics

AS BAY DOORS ARE OPENED, EVEN IF THE AIRCRAFT IS FLYING IN A STEADY ATTITUDE,

FLOW INSIDE THE CAVITY BECOMES HIGHLY UNSTEADY AND EXTREMELY COMPLEX

ASSOCIATED PROBLEMATICS

►UNSTEADY FLOW FIELD – RANDOM FLOW OSCILLATIONS DURING STORE

RELEASE PROCEDURE FROM THE AIRCRAFT

►LONGITUDINAL PRESSURE GRADIENT – PITCHING MOMENTS INDUCED ON

THE STORE ALTERING ITS DROPPING TRAJECTORY

►HEAVY ACOUSTIC LOADS - OVERALL SOUND PRESSURE LEVELS IN

EXCESS OF 160 dB WITH PARTICULAR RESONANT MODES CAPABLE OF

POWER LEVEL UP TO 180 dB


Weapon Bay Aerodynamics


Approach to the Problem

ACTIVE CONTROL METHODS

(SPOILERS, BLOWING, ETC…)

FLOW CONTROL TECHNIQUES

STRATEGIES

CAVITY SHAPING (SLANTED WALLS,

ALTERATION OF INCOMING BOUNDARY

LAYER, ETC…)

FOCALISED ON ALTERING THE

TRAJECTORY OF THE SHEAR LAYER,

DIVERTING IT OUTSIDE THE CAVITY

AIMED TO ALTER THE STATUS OF THE

SHEAR LAYER INSIDE THE CAVITY


Approach to the Problem – Active Control Methods

ADVANTAGES

►GOOD PERFORMANCES

►NO ALTERATION OF THE SHAPE OF THE CAVITY

DISADVANTAGES

► PERFORMANCES MAY DETERIORATE IF OPERATION ARE OUTSIDE THE

DESIGN POINT

► INCREASED COMPLEXITY ON THE DESIGN DUE TO MOVING PARTS


Approach to the Problem – Cavity Shaping

ADVANTAGES

►ABSENCE OF MOVING MECHANISM

►GOOD PERFORMANCES OUTSIDE THE DESIGN POINT

DISADVANTAGES

► ALTERATION OF CAVITY SHAPE

► INFLUENCE ON AIRFRAME EXTERNAL DESIGN


Weapon Bay Design - Flow Chart

AIRFRAME INSTALLATION

INTEGRATION

WITH AIRFRAME

AERODYNAMIC

AND

STRUCTURAL

REQUIREMENTS

BAY OPENING

LIMITED TO FEW

SECONDS

COMPLIANCE

WITH RCS

REQUIREMENTS

INTEGRATION OF THE WEAPON BAY IN

THE PLATFORM DESIGN

SIMULATION OF COMBAT ENGAGEMENT

CONDITIONS

INCIDENCE,

SIDESLIP, AND

DYNAMICS

EFFECTS


Actual Study

REALISTIC CAVITIES ALWAYS

INCLUDE STRUCTURAL RIBS

PREVIOUS STUDIES (KNOWLES ET AL. 2015) INDICATED THAT RIBS

COULD HAVE A BENEFICIAL EFFECT ON THE FLOW INSIDE THE CAVITY

COLLAR: EXTENDED INTERNAL RIB WITH A

SUITABLE ARRANGEMENT CAPABLE TO CONTROL

THE PRESSURE-FLUCTUATION LEVELS

DEVELOPMENT OF AN INNOVATIVE

CAVITY FLOW CONTROL TECHNIQUE


Collars Geometry

► SPANNING FULL WIDTH AND DEPTH OF CAVITY

► INCORPORATING A CUT-OUT TO ACCOMMODATE STORE/S

► VARIOUS GEOMETRIES, STRAIGHT, YAWED, AND LEANED

► TEST INCLUDED COLLARS MANUFACTURED BOTH IN MACHINED STEEL AND 3D PRINTED

SIMPLE PLASTIC

► INITIAL STUDY CONDUCTED ON 5 POSSIBLE POSITIONS (25%, 33%, 50%, 67%, 75 % OF

CAVITY LENGTH)

Yawed StraightBackward

Leaned


Collars Geometry


SHRIVENHAM EJECTOR-DRIVEN TRANSONIC WIND TUNNEL:

►206 mm (H) x 208 mm (W)

►CAVITY MOUNTED IN SIDE DOOR FLUSH WITH WALL

►27 PRESSURE TAPPINGS ON CAVITY’S FLOOR

►ALL TESTS AT MACH 0.86 AND EQUIVALENT PRESSURE ALTITUDE OF 12000 ft

Experimental Setup


Cavity Geometry

RECTANGULAR CAVITY

► L=160 mm, W=32 mm, D=32 mm

► L/D=5, W/D=1

MISSILE MODEL

► REPRESENTATIVE OF A TYPICAL AIR-TO-AIR WEAPON

► BLUNT TANGENT OGIVE WITH LENGTH/DIAMETER=18

► MOUNTED CENTRALLY INSIDE THE CAVITY


Results 1/4OVER 40 COMBINATIONS TESTED

FOUND 2 OPTIMUM SOLUTIONS

5 STRAIGHT COLLARS

(25% 33% 50% 67% 75%)

2 STRAIGHT COLLARS (25% 33%)

+

2 BKW LEANED (50% TO 67% AND 67% TO 75%)


Results 2/4

Mean Flow – Pressure Coefficient - Centreline

Plot has been removed for Copyright reasons. For further informations contact

the autor

Bacci David

[email protected]

+393490563016

mailto:[email protected]


Results 3/4

Mean Flow – OASPL - Centreline


the autor

Bacci David

[email protected]

+393490563016



Results 4/4

Non-Stationary Flow – SPL at x/L=0.9, 2y/W=0.0


the autor

Bacci David

[email protected]

+393490563016



►COLLARS APPEAR TO MODIFY OR SUPPRESS MANY OR ALL CAVITY TONES AND

REDUCE THE BROADBAND NOISE LEVELS

►COLLARS EFFECTIVENESS DEMONSTRATED BOTH WITH STORE PRESENCE AND

ABSENCE INSIDE CAVITY

►POTENTIAL ADVANTAGES OVER METHODS THAT INVOLVE EXTERNAL SPOILERS,

DEFLECTORS OR BLOWING IN THAT NO ACTUATION IS REQUIRED. ADDITIONALLY THIS

SOLUTION COULD BE INSTALLED IN ALREADY COMPLETED DESIGN

►3D PRINTING, USING PLASTIC, ENABLE EASE OF MANUFACTURING, LIGHT-WEIGHT, AND

POSSIBILITY TO ADAPT COLLARS GEOMETRY TO WHICHEVER CAVITY/STORE

COMBINATIONS POSSIBLE

Conclusions


►STUDY THE IMPACT OF COLLARS ON AIRFRAME DRAG

►COLLAR PERFORMANCES WITH INCIDENCE, SIDESLIP, AND DYNAMICS EFFECTS

►IMPROVEMENT TO THE COLLAR PERFORMANCE BY LOCAL GEOMETRY MODIFICATIONS

Future Work


www.cranfield.ac.uk

Thank You

design of weapon bays for stealth aircrafts...3 © cranfield university 2017 weapon bay aerodynamics...

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